IMRT: State of the Art

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Radiation therapy is reaching new heights with IMRT. Addressing one of the major problems of conventional treatments, IMRT can deliver lethal dosages of radiation to tumors while sparing adjacent, critical structures. This means higher cure rates for patients, less complications and the ability to lead a more normal life during treatment. Radiation oncology professionals are leveraging the power of IMRT; treating brain, head and neck and prostate tumors, and exploring treatment for tumors of the kidney, breast, pancreas, lung, spine and cervix.

Intensity modulated radiation therapy (IMRT), an extension of conformal therapy, is highly precise, high-dose radiation therapy that targets cancer cells, while minimizing the exposure of nearby healthy tissue. The treatment option employs powerful inverse planning software to plan a precise dose of radiation in three dimensions, based on individual tumor size, shape and location. The delivery system then directs radiation at the tumor and modulates the intensity of pencil-thin beams of radiation with laser accuracy.

The combination of computer power and linear accelerator (linac) results in exquisite dose painting, says Richard Stark, director of Varian Medical Systems' delivery systems product line. "If you can deliver the dose very, very precisely, then you have the opportunity to reduce rates by reducing the dose to surrounding critical structures," he continues. "You also can increase the dose to your target volume without increasing the side effects."

Take, for example, IMRT as a treatment option for localized prostate cancer. It provides a higher radiation dosage to the prostate gland, while reducing the dosage reaching the rectum and bladder, potentially minimizing painful physical side effects.

"Prostate and head and neck cancer were the very first thing people attacked with IMRT," explains Stark. "What we are seeing in the literature is that it is being used in more and more places. You can use it in the lung. You can use IMRT for treatment of the pelvis, such as for cervical cancer." The University of Chicago Hospitals, one of the first medical centers to start treating gynecologic cancers in 1999 with IMRT, has treated more than 150 patients, according to Arno Mundt, MD, associate professor of radiation and cellular oncology at the University of Chicago and University of Illinois.

Jack Yang, PhD, chief medical physicist, radiation oncology, at the 527-bed Monmouth Medical Center in Long Branch, N.J., part of the Saint Barnabas Health Care System, says the radiation oncology department treats a lot of head and neck cancers with IMRT. Patients have experienced less side effects. "We spare the parotid gland and the patient is able to carry on the same function as they had before," explains Yang. "In the past, one of the side effects for radiation treatment has been destruction of the parotid glands and the patient will have a dry mouth symptom for life."

Yang emphasizes that IMRT opens the door for re-treatment. "Some patients who go through radiation treatment reach a tolerance on certain critical structures," says Yang. "The tumor may come back. What can you do? In the past, we could not do anything. With IMRT, we can take care of the tumor without overdosing the critical structure."

THE LEARNING CURVE

The therapeutic success of IMRT has fueled widespread adoption. In the United States, radiation oncology departments and free-standing cancer treatment centers are realizing that state of the art means IMRT. At the same time, the technology does not replace conventional radiotherapy methods - it is typically used to treat 30 to 40 percent of cancer patients.

One of the reasons boils down to what has been dubbed an obvious drawback of IMRT - the arduous nature of the technology. Since it is time-intensive, physicians will use IMRT when they want to control the dose from hitting critical structures or to treat tumors that are unreachable otherwise. Successful IMRT also requires a well-trained and large staff that includes radiation oncologists, medical physicists, dosimetrists and radiation therapists - positions which are often hard to recruit and keep filled.

The standard for IMRT planning requires CT scanning for image-based calculations and treatment. Planning software now provides fusion capability and radiation oncologists may spend a little more time overlaying CT scans with MRI or PET data to better define the target volume. Once the physician chooses the dose